The storm classification table below has been developed by scientists
at the University of Virginia for assessing the relative power of northeasterly
storms in the west-Atlantic. The severity of such storms depends on wave
height, which not only depends on wind strength but also on its duration
and fetch, all necessary conditions to reach a 'fully
developed' sea state. Note that the wind speed is absent from this
table.

Class1weak

Class 2moderate

Class 3significant

Class 4severe

Class 5extreme

Average peak wave height (m)

2

2.5

3.2

5

7

Average duration (hr)

8

18

34

63

96

RelativeFrequency (yr)

49.7% (2yr)

25.2% (4yr)

22.1% (5yr)

2.4% (40 yr)

0.1% (1000yr)

Beach erosion

minor

modest

across beach

severe

extreme

Dune erosion

none

minor

significant

erosion andrecession

destruction

Overwash

none

none

none

severe on low-profile beaches

region-wide

Propertydamage

none

modest

local

community-wide

region-wide

Notes: a relative frequency of 50% means one such storm every two years.
0.1% once every 1000 years.
Adapted from Cornelia Dean 'Against the tide, the
battle for America's beaches'. 1999. Columbia University Press